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Monza 300 centerless grinder wiring


Jul 31, 2017
Washington state
I purchased a Monza 300 centerless grinder from a shop that reconfigured the wiring for high voltage 440v, in my shop I run low voltage 220v and want to restore the original low voltage configuration.

Does anyone own this model of grinder connected to 220v? could you please share a photo of the 7.5HP grinding spindle motor terminal connections.

I have hired a electrician who specializes in control systems to perform the voltage conversion, the 4 other electric motors were easy for him to switch over.
But the main spindle motor is a lot more complex, it starts in Wye then switches to Delta after 15 seconds.
No electrical schematics are available for this grinder, The motor has 12 leads and most of them are unlabeled. The motor nameplate also has no instructions.
The person who rewired the machine 10 years ago left no documentation of what he changed, he also intentionally scratched out part of nameplate.

My electrician suggested asking if anyone else is using this machine with 220v and could provide photos or more documentation. He is also trying to find more information for these European motors.
The machine was made in Italy around the late 70s or early 80s.

Here is a photo of the grinder.IMG_1788.jpeg

Here is the electric motor nameplate

Here are the spindle motor terminals as they are configured for high voltage.

Thank you for the help.
You can do some experiments to determine the correct 220 volt winding connections. Let me know if you want to try.
My guess is that the center block contains the interconnect between the 2 separate 220 windings of each phase. It is likely that the copper bar that connects the 2 center terminals together needs to be changed. You remove the bar (possibly 2 bars stacked) and connect the 2 upper terminals with a bar and connect the 2 lower terminals with the second bar (if there is one). Do this for each of the three phases. If you get this wrong, it will act as a dead short and pop your circuit breaker. If the breaker is properly sized, you "should" not cause any damage.
If you don't want to try my "guess" then I can explain how to do the experiment.